highlight cell if previous column meets specific condition R

Question

I have a dataframe

library(flextable)
df = structure(list(col1 = c(1, NA, 1, 1, 1), col2 = c(NA, 1, NA, 
1, 1), col3 = c(1, 1, NA, 1, NA), col4 = c(1, 1, 1, 1, NA)), class = "data.frame", row.names = c(NA, 
-5L))
df %>% flextable()

I want

to return the last 3 columns highlighted based on the following logic:

• red if it is blank
• green if and only if the preceeding column was blank.

Based on this, I am trying to create a color matrix to identify the green highlights, but have hit a brick wall.

To identify the red matrix, I used the following code ifelse(is.na(df),"red","").

what would be the best method to identify the green labels

Answer 1

Not the prettiest, but works

df=data.frame(col1 = c(1,NA,1,1,1,1),
              col2 = c(NA,1,NA,1,1,1), 
              col3 = c(1,1,NA,1, NA,1),
              col4 = c(1,1,1,1,NA,1))
df %>% flextable()
red = ifelse(is.na(df),1,0)
green = data.frame()
for(n in 1:(ncol(red)-1)){
  print(n)
  r=ifelse(red[,n]==1 & red[,n+1] == 0,1,0)
  green = rbind(green, r)
}
green = t(green)
colnames(green) = paste0("col",2:4)
green
red[,2:4]
ft = df[,2:4] %>% 
  flextable() %>%
  bg(i = ~ is.na(col2), j = 1,bg='red') %>%
  bg(i = ~ is.na(col3), j = 2,bg='red') %>%
  bg(i = ~ is.na(col4), j = 3,bg='red') %>%
  bg(i = ~ green[,1]==1,j = 1, bg='green') %>%
  bg(i = ~ green[,2]==1,j = 2, bg='green') %>%
  bg(i = ~ green[,3]==1,j = 3, bg='green')
ft